The present invention relates generally to digital X-ray imaging and more particularly to panoramic digital X-ray imaging in the field of dental diagnostics.
Conventional apparatus and methods for obtaining a panoramic X-ray image or radiograph or X-ray shadow of the maxillo-facial region utilize rotational panoramic radiography using an external X-ray source. This is accomplished by allowing a narrow vertical X-ray beam to move in a transverse plane around a rotational axis which is positioned inside the mouth of the patient. The X-ray image of the maxillo-facial region is projected on a radiographic film. The radiographic film is moved in the transverse plane and also relative to the X-ray beam. Because of the uneven curvature of the maxillo-facial complex, the film speed is varied to match the vertical and horizontal magnifications of the X-ray projection. This technique provides a relatively undistorted X-ray image of the maxillo-facial area on a radiographic film.
Several manufacturers currently market radiography machines (X-ray machines) that produce high quality (relatively undistorted) panoramic radiographs of the maxillo-facial region. All of these machines use a rotating X-ray beam and a moving film. The center of rotation for each type of machine can vary. Some machines utilize a fixed center of rotation, some utilize a continuously moving center of rotation, and yet some others utilize a combination of the two. However, each type of machine utilizes a predetermined scanning geometry, film speed, focal spot size and X-ray beam width. The combination of these parameters produces a unique image layer for each rotational-type panoramic radiography equipment. The image layer has a central plane for which the X-ray image is sharpest and least distorted. The manufacturers of such equipment have attempted to design an image layer which conforms in its overall geometry to the structure of the dental arch, which is sufficiently wide so as to provide a reasonably sharp portrayal of that anatomy.
Although these systems provide sufficiently undistorted radiographs, they still require the use of photographic films and photographic processing and developing equipment to produce the image of an object. As a result, the users of these radiography equipment must still deal with cumbersome and expensive film processing equipment. With the availability of high resolution electronic radiation detectors, and with the advancement of digital signal processing and imaging techniques, it has become possible to create and store X-ray images digitally. Such systems do not use X-ray films. Various sensors and techniques have been developed to produce digital X-ray images. The present invention provides an apparatus and a method for obtaining digital panoramic X-ray radiographs by utilizing a linear sensor array with variable data acquisition periods in order to provide an image with proper proportion both in the horizontal and vertical dimensions.